Hollow rivet with undercut head



Dec. 27, 1949 E. E. NOFZINGER HOLLOW RIVET WITH UNDERCUT HEAD 4 She ets-Sheet 1 Filed Jan. 9. 1942 4 7 2 m a x a F "H. A A 3 l a a w l M? l I z\ M a I IOA INVENTOR MCIKW BY 6M4 w v ATTORNEY Deco 27, 1949 E. E- NOFZINGER I v HOLLOW RIVET WITH UNDERCUT HEAD 4 Sheets-Sheet 2 Filed Jan. 9. 1942 INVENTOR.

HTTORNE Y E. E. NOFZINGER HOLLOW RIVET WITH UNDERCUT HEAD Dec. 27, 1949 4 Sheets-Sheet 3 Filed Jan. 9. 1942 FIG. 2/

INVENTOR.

ATTORNEY Dec, 27, 1949 E. E. NOFZINGER H6LLOW RIVET WITH UNDERCU'I. HEAD 4 Sheets-Sheet 4 Filed Jan. 9, 1942 INVENTOR.

ATTORNEY Patented Dec. 21, 1940 2.49%.! HOLLOW amrr WITH UNDEBCUT READ or! I. Nohinger, Grcenville, Mich, assignor to United Air Lines. Ina, Chicago, 111., a corporation of Delaware Application Ionian 9, 1942, Serial No. 426.104

' Claims. (01. 85-40) This invention relates to the art of riveting. More particularly, it relates to a novel form of rivet adapted for enlargement of the blind end thereof by force applied from the head end thereof.

In many cases, particularly in airplane fabrication, it is impossible to obtain access to both sides of a plurality of plates which are to be riveted together. Consequently, many attempts have been made to devise a method of riveting in which the rivets can be inserted, and the shank end thereafter enlarged, by a single operator working from one side of the parts which are to be fastened together. These attempts have not been entirely successful for a number of reasons. Tubular rivets have been used but the manner in which they have been expanded has required the employment of relatively thin walled rivets, and such rivets have a low resistance to shear. Furthermore, in many instances the parts which are being riveted are not forced tightly against each other to increase the shearing strength of the joint by the frictional contact between the parts. Another disadvantage .to previous modes of riveting has been the excessively high cost of the special rivets required.

I have discovered that the well known action upon a closed cylinder of fluid pressure applied to the inside of the cylinder can be advantageously utilized in the art of blind riveting. when fluid pressure is applied to the interior of a closed cylinder, the walls of the cylinder are expanded circumferentially and shortened axially. That is to say, the cylinder tends to assume the shape of a sphere.

In applying this principle to the art of riveting, I employ a rivet having a head and a shank pro vided with a cavity having a single access opening. Fluid under pressure is forced into the cavity by fluid pressure apparatus including a nozzle inserted in the access opening. By regulating the amount of pressure employed and properly selecting the material and the proportions ofthe rivet, the desired degree of expansion or enlargement of the shank can be obtained without rupturing the rivet.

When the rivet is properly designed as to length and circumference of the shank in relation to the thickness of the wall to which it is to be secured and the size of the opening in which it is to be received, the shank of the rivet can be expanded to completely fill the opening, to enlarge the rear end of the shank, and to pull the enlarged rear end of the shank against the wall'so that there 2 to the rivet is a firm engagement between the rivet and wall at all points of contact between the two. v

By forming the rivet so that the single access opening to the cavity in the shank is located in the head of the rivet, the entire riveting operation can be performed from one side of the work.

The principal object of the present invention is to provide a novel form of rivet adapted for use in the manner indicated above.

This object and others ancillary thereto will become more clearly apparent in the following specification, when read in connection with the accompanying drawings, wherein:

Figure 1 is a sectional view of a rivet embodying the present invention illustrating the manner in which a fluid pressure nozzle may be attached thereto;

Figure 2 is a sectional view of a modified form of rivet;

Figure 3 is a sectional view illustrating the manner of applying a fluid pressure nozzle to the rivet of Figure 2; a

Figure 4 is a sectional view illustrating an alternative method of applying a fluid pressure nozzle of Figure 2;

Figure 5 is a sectional view illustrating the relation between a rivet and a wall structure before the rivet has been expanded; and

Figure 6 shows the structure of Figure 5 after the rivet has been expanded;

Figures 7 to 27 inclusive illustrate modified forms of rivets and modified applications of the rivet to wall structures.

Various different forms of rivets and difierent methods of applying fluid pressure thereto may be utilized within the scope of the present invention.

Figure 1 illustrates a simple form of rivet III .which comprises a head ii and a shank l2. The head and-shank of the rivet are provided with a cavity I: having a single access opening in the head end thereof. The interior of the head Ii which defines the portion of thecavity located therein is threaded as indicated at ll to receive a threaded nozzle ii, by means of which fluid under pressure may be introduced into the cavity H by a suitable fluid pressure supplying device to be described later. Nozzle i5 is provided with an internal bore or passageway shown in dotted lines, and is preferably connected to the pressure supplying device by a swivel connection whereby the nozzle may be rotated to permit engagement with and disengagement from the rivet.

In a structure having the characteristic dimensions hereinafter described, I have found that a accuse leak tight joint can be obtained between the nozzle l5 and the rivet In by using a standard screw thread with a taper of fifteen to twenty thousandths of an inch per inch of length with the rivet being tapped to a depth of four or flve threads. Any suitable means may be employed for threading the rivet onto the nozzle, preferably before the rivet is inserted the opening to which it is to be secured; After the rivet has been expanded the nozzle I5 is detached from the rivet.

Figure 2 illustrates a slightly modified formof rivet la in which the head .of the rivet has been upset about the opening to the cavity l3a so as to provide an annular radially inwardly extending flange l6 having a small central opening therein. Preferably the diameter of the punch which upsets the head to provide the flan ge I6 is approximately 80% of the outside diameter of the rivet shank. Except for replacing the threads-I4 with the flange l 6, rivet l0a-is identical to rivet [0.

This form of rivet lends itself to the use of a diflerent form of fluidpressure applying nozzle I in the manner shown-in Figu e 3. As there shown, the nozzle I 8 includesa tapered outlet end l8b adapted to be pressed into the small opening defined by the flange l6 so as to provide a fluid tight joint therewith. In this form of the invention the outlet 18b is made of harder material than the rivet so that by pressing the outlet into the opening in flange IS the flange is deformed suificiently to provide a fluid tight joint.

Nozzle l8 consists of a body portion i8a adapted to be connected to a pump,. and a tapered outlet end I8b. Part l8b is preferably in the form of small drawn tubing and is secured within the bore of body l8a by soldering or brazing. The tapered end of outlet lab is of extremely hard material highly polished. One advantage of this construction is that the nozzle need not be accurately aligned axially with the rivet. By jamming the hardened and tapered end l8b into the'opening in flange IS, the flange is deformed to snugly engage the outlet I8b regardless of poor alignment. The method of forcing fluid into the rivet which is shown in Figures 2 and 3 has the advantage over that shown in Figure 1 of being much faster to operate. A shorttim'e-is required to thread rivet I0 to nozzle I and then unthread these parts after the rivet has been expanded. Less time is required to insert or remove nozzle l8. Due to the small size of the opening in flange l8 and the small size of the tapered end of nozzle I8, there is very little back pressure against the nozzle when fluid is forced under pressure into cavity l3 through nozzle I8. I have found that with a rivet having an external diameter of inch and an internal diameter of 42% of the outside diameter which is formed of -l 1 ST aluminum alloy, and a nozzle of a diameter of twenty thousandths of an inch at the point and having a taper between and a thrust pressure of twenty to thirty pounds is sufficient to hold the nozzle in place and maintain a leakproof connection during the expanding operation where the maximum expanding pressure is in the neighborhood of 100,000 pounds per square inch. The same results are obtained with rivets of other sizes, providing the proportions are the same.

Figure 4 illustrates a modified method of attaching the nozzle iii to the rivet I'Oa which may advantageously be employed when large rivets are used. In this modification the rivet is provided with a notch or recess at diametrically spaced points about'the periphery of the head Ila adapted to receive a pair of holding clamps I9. The nozzle ll forms a part of a fluid pressure applying device which includes a housing 20 and a sleeve 2| threaded into the housing. The

sleeve 2| has an annular flange 22 which forms one abutment for a coil spring 23. An annular ring 34 surrounds sleeve 2| and is normally held in retracted position (to the top) by the spring 23. i loldingclamps is are pivotally connected to "the-ringtl at 38. The" free'end of the clamps l0 l9 are adapted to engage the notches in the head Ila of rivet i011 as shown in Figure 4. The other end of the clamps extend parallel to the axis of the ring 34 and are received in slots 35 in the ring so that theclamps may pivot around the pivots 36. Springs 31 carried by ring 34 are provided-to normally hold the clamps in the position shown in Figure 4.

The fluid pressure applying device illustrated in-Figure 4 is connected to the rivet as there shown by manually pressing the rear ends of the clamps l9 toward each other so as to spring apart the free ends of the clamp. The nozzle I8 is then inserted into the opening in the flange l0 and the ring 34 pressed forwardly. Pressure on the rear ends of the clamps is then released to permit the free ends of the clamps to spring into the notches or recesses in the head of the rivet. 'The coil spring 23 maintains the free ends of the clamps IS in engagement with the head of the rivet and the nozzle l8 in proper position. After the rivet has been expanded in the manner which will be described later, the nozzle i8 is released from the rivet by again pressing the rear ends of the clamps l9 toward each other, whereupon the fluid pressure applying device may be withdrawn from' the rivet.

From the foregoing it will be seen that various methods and structures may be employed for forcing fluid under pressure into the cavity of the rivet whereby to expand the rivet in a manner to be described later. Of course, after the desired expansion has taken place the fluid pressure applying mechanism is detached from the rivet which has been expanded so as to make it available for use in expanding another rivet. In each instance the nozzle is held within the access opening to the cavity so as to provide a fluid tight connection therewith and thereby. obtain the full benefit of the pressure resulting from forcing fluid into the cavity through the nozzle.

Figures 5 and 6 illustrate the method of applying the rivet of Figure 1 to a wall structure consisting of a pair of plates 38 and 39 having aligned openings 40 and II respectively formed therein. In the construction shown in these figures the rivet is formed of material which is softer than the material of plates 38 and 39.

The original configuration of the rivet I0 is shown in Figure 5. The rivet may be formed of steel or aluminum allo and may have, for ex ample, an external shank diameter of one-eighth inch. Other diameters may be used as well. The diameter of the shank I2 is less than the diameter of the openings 40 and 4| so as to permit convenient insertion of the rivet into the opening. I have found that a clearance between the rivet shank and the plates of 5% to 10% of the diameter of the shank is a practical clearance, both from the standpoint of ease of insertion and from the standpoint of expanding the rivet to completely flll the openings 40 and II.

' The diameter of the cavity It may vary considerably, but I have found that for best results it should be somewhere between twenty-five and forty-five percent of the outside diameter of the rivet. A cavity of less diameter requires excessive pressure for expansion, while a larger cavity decreases the thickness of the shank wall and thereby reduces the shearing strength of the rivet and also permits possible rupture of the shank wall. In this particular embodiment the diameter of the cavity is 42% of the outside diameter of the shank.

When the back face of the head ll engages the front face of plate 38 the cavity should extend beyond the back face of plate 39 sufliciently so that the mid-point of the cavity within the shank lies in a radial plane located rearwardly of therear face of plate 38 when the plates are of equal thickness as here shown. Whether or not the mid-point should lie in a plane rearwardly of the rear face of plate 39 will depend upon the dimensions of the parts and the particular characteristics desired in the riveted joint. For example, when the thickness of the plates is relatively small as compared to the inside diameter of the shank, a relatively greater proportion of the shank length should project beyond the rearmost plate in order to provide ample material for expansion into the head to be formed at the shank end, in which case the mid-point of the cavity the rear face of the rear plate. When the plates are quite thick and the total length of the rivet shank must therefore be relatively great, however, the necessary rearward projection of the cavity may suitably be less than what would be required to bring the mid-point thereof beyond the rearmost plate surface. To describe a proper proportioning more specifically, I have found that a satisfactory relationship can be obtained where the cavity l3 projects beyond the rear face of wall 39 from a distance equal to the inside diameter of the shank l2 to a distance equal to two and one-half times the inside diameter of the shank. In the embodiment of Figures and 6, the mid-point of the cavity is shown as being located slightly behind the rear face of the plate 39 (see dotted lines in Figure 5), and the cavity l3 extends beyond plate 39 a distance equal to two and'one-half times the inside diameter of the shank I2. I have found from experimentation that for best results the cavity in a V; inch rivet should extend beyond the rear face of the wall structure a minimum of .075 inch, and proportionately for other sizes.

Fluid under pressure is introduced into' the cavity l3 by screwing thereinto a nozzle l5 forming a part of a fluid pressure device as previously described in connection with Figure 1. The connection between the nozzle l5 and the rivet is such as to produce a fluid tightjoint at pressures up to approximately 150,000 pounds per square inch. The exact pressure necessary to expand a given rivet will need to be found by experimentation. Rivets of the character described above require and will withstand pressures between '75,- 000 and 125,000 pounds per square inch.

As fluid is forced into the cavity l3 under pressure, there is a tendency for the rivet shank to assume a spherical shape. As pressure is applied the shank .bulges outwardly, the greatest expansion initially occurring at the mid-point of the cavity, that is, slightly beyond the back face of plate 39. (See dotted lines-Figure 5.) As the pressure increases the wall of the shank in the rear of the back face of plate 39 will bulge outwardly still more and the edge of plate 39 which defines the opening I therein will shear into the rivet to form a slight projection inthe may lie rearwardly of rivet indicated at 42', Figure 6. At the same time, the wall of the shank near the head will be expanded so that the shank completely fills the opening 4| in the plate 39 and completely fills all but a small portion of the opening 40 in plate 38.

Since the wall of the shank I2 is expanded and the volumethereof must remain the same, there is a tendency for the metal to flow axially and thereby shorten the rivet. The relative len ths of the rivet before and after expansion are shown in Figures 5 and 6. Before the length of the'i'ivet is decreased appreciably, the rivet grips the back face of the plate 39. Thus, when the-rivet contracts further in length the two plates 38 and 39 will be pulled tightly together, thereby producing a substantial frictional contact between the two plates.

When the rivet ID has been expanded to the configuration shown in Figure 6, the fluid pressure on the cavity is released and the nozzle l5 detached from the rivet.

The construction .shown in Figures '1 and 8 is identical to that shown in Figures 5 and 6, with the exception that the shank l2 shown in Figures 7 and 8 is shorter than the shank shown in Figures 5 and 6. In this embodiment the cavity l3 extends beyond the wall 39 a distance equal to the inside diameter of the shank l2. The results of utilizing the shorter shank are graphically illustrated by the dotted lines in Figure '7, from which it will be noted that the mid-point of the cavity within the shank lies in a radial plane located forwardly of the rear face of plate 39, and the greatest expansion initially occurs in that plane.

I have found from experimentation that the length of the shank l2 may be such asto locate the mid-point of the cavity within the shank as shown in either Figure 5 or '7, or at any intermediate position between the locations shown in those figures, with good results. These are not to be considered as limitations, however. Where the mid-point is located as shown in Figure 7 the rear edge of the plate 39 will bite further into the outer surface of shank I! when the rivet has been expanded, as shown at 43 in Figure 8.

The construction of Figure 7 has the advantage over the construction of Figure 5 of providing greater resistance to withdrawal of the rivet after it has been expanded. On the other hand, the wall thickness of the shank in Figure 7 has been reduced to a greater extent than in Figure 5, and the construction of Figure '7 therefore provides less resistance to shear and bearing loads than the construction of Figure 5. Probably the ideal construction lies some place between these two limits, both of which are satisfactory.

The results of employing a rivet ID with plates 38 and 39 which are made of softer material than the rivet are illustrated in Figures 9 and 10. As there shown, the shank I! of the rivet presses against the sides of the openings in the plates 38 i and 39 so that the opening in plate 39 is materially enlarged and the opening 40 in plate 38 is slightly enlarged adjacent the rear face of the plate forming a tapered opening through the plate of decreasing diameter from the rear to the front. Thus, when the wall of shank l2 expands under the pressureof fluid introduced thereinto, the plates 38 and 39 are gripped between the bulge in the shank l2 and the head ll just as satisfactorily as when the plates are harder than the rivet. An advantage of this construction is 7 that no abrupt change in wall thickness or the shank i2 occurs.

From the foregoing it will be apparent that the present invention provides a satisfactory connection regardless of whether parts 38 and 38 are formed of harder or softer material than the rivet In. In either case, the parts are tightly gripped between the head i of the rivet l and the expanded shank end thereof.

By reference to Figure 6 it will be noted that the shank I2 is not expanded adjacent the head sufficiently to completely fill the opening 40 in plate 38. As will be recognized, it is desirable that the shank l2 completely fill both the openings 40 and 4|. slightly modified form of the rivet Illa which may be employed to accomplish this desired result. In this modification the head of the rivet is undercut as indicated at 44 so that the shank |2a isfree to expand adjacent the front face of plate 38 and thereby completely fill the opening 40 in that plate. The rivet Na in Figures 11 and 12 is shown as including the internal flange l6 adjacent the access opening to the cavity I311. The cavity in the shank extends beyond the rear face of plate approximately 1.5 times the diameter of the shank. Otherwise, excepting for the undercut at 44, the construction shown in these figures is identical to the construction shown in Figures and 6.

An alternative form of rivet Illa which may be employed to permit the expansion of the shank |2a so as to completely fill the openings 40 and 4| is illustrated in Figures 13 and 14. The construction there shown is identical to that shown in Figures 11 and 12 except that the undercut, 44 has been eliminated and the outer surface of the shank |2a is tapered from the point of attachment to the head Ha to a point near the rear face of plate 38, the largest diameter being adjacent the head and the diameter at that point being substantially equal to the diameter of the opening 40 in plate 38. Thus, when the shank of the rivet Illa is expanded as heretofore described, the shank will completely fill the openings 4|) and as clearly shown in Figure 14. It will be readily apparent that this construction does not interfere with the convenient insertion of the rivet into the openings 40 and 4| while at the same time providing for the complete filling of those openings by the shank when the latter is expanded.

In Figures 15 and 16 there is shown a construction which is identical in every respect to the construction shown in Figures 11 and 12, with the sole exception that the external surface of the shank |2a is serrated as indicated at 45 and the rivet, or at least the external surface of the shank, is preferablyharder than the plates 38 and. Thus, when the rivet is expanded as previously described, the serrations 45 bite into the plates 38 and 39 and aid in looking the plates together and in securing the rivet thereto (see Figure 16).

The modified form of structure shown in Figures l7 and 18 is identical to the construction shown in Figures 15 and 16 except for the fact that in place of the serrations 45 there is provided a sleeve 48 of hardened metal having serrations 48a on the external surface thereof and a radial flange 46b at one end thereof. The sleeve 46 is preferably split axially to facilitate the expan sion thereof. It is inserted in the openings 40 and 4| either with the rivet or before the rivet, and with the fiange 46b located between the head He of the rivet and the front face of plate 38. A sleeve, such as 48, may be employed without ser- Figures 11 and 12 illustrate a rations. In that event, the hardened sleeve merely serves to increase shear strength.

In this modification the clearance between the rivet and the peripheries of openings 40 and 4| will be greater than the diameter of the shank 2a which has previously been described, in order to accommodate the sleeve 46. In all other respects the relationship of the parts and the method of attaching the rivet to the plates 38 and 39 is identical to that previously described. With the construction shown in Figures 17 and 18 it will be understood that when the rivet no is expanded the sleeve 46 is likewise expanded and the ser rations Mia-bite into the portions of the plates 38 and 39 which define the openings 40 and 4| therein so as to securely lock the rivet assembly to these parts. The characteristic deformation of the rear end of the shank |2a is not materially affected by the use of the sleeve 46, as clearly shown in Figure 18. This construction has the advantage over constructions of Figures 15 and 16 that the rivet may be soft enough to expand readily and the sleeve hard enough to provide a good biting engagement with plates 38 and 39. This construction provides a good balance between desirable shear strength and pressure required for expansion.

Figures 19 and 20 illustrate a rivet 0b generally similar to but of slightly different configuration than the rivet l previously described. In this modification the shank |2b is formed so as to initially provide a cavity 13b of decreasing diameter from the head-toward the closed end diameter.

thereof. The outside of the shank is of uniform The decrease in internal diameter is proportioned so as to provide a cavity 3b of substantially uniform internal diameter after the shank has been expanded in the manner previously described in connection with Figures 5 and 6. Within the cavity |3b the head ||b is threaded as at |4b to receive a fluid pressure applying nozzle, such as the nozzle l5 illustrated in Figure 1. After the rivet has been expanded a plug 41 having threads 48 is inserted in the cavity 3b and threaded home as shown in Figure 20, so as to substantially fill the cavity |3b in the region of the plates 38 and 39, By the employment of the plug 41 the shearing strength of the rivet can be increased and the rivet endowed with the properties of a solid shank type of rivet. The head of the plu 41 may be of any convenient or desired form. As here shown, it is provided with a slot 49 to receive a rotating tool, such as a screw driver, to permit the threading of the plug into the cavity I3b. It will be obvious, of course, that other forms of plugs may be employed, such for example as a plu which is of the drive in type.

The modified form of construction shown in Figures 21 and 22 is identical to the construction I shown in Figures 11 and 12 except that in this modification the external surface of the shank |2a is provided with an annular groove 50 located substantially in alignment with the rear face of the plate 39 when the rivet is installed in the openings 4|! and 4| and before expansion (see Figure 21) Thus, when the rivet is expanded as previously described, the shoulder formed by the rear face of the groove 58 embraces the rear face of plate 39, as indicated at 5| in Fig. 22. The principal advantage of the groove 50 is to weaken the wall of the shank |2a at the desired point so as to minimize the pressure required to effect the necessary expansion to effectively lock I ing the openings the difference resulting the rivet to the plates 38 and 39 and to assure good holding power of the rivet. The advantages of this construction may be increased by enlar 40 and 4| to provide a taper of decreasing diameter from the rear face of plate 39 to a point slightly forwardly of the rear face of plate 38, as shown in Figures 21 and 22. This reverse tapering of the opening in which the rivet is installed may be advantageously employed in other modifications also. 1

The modification shown in Figures 23 and 24 illustrates a rivet 52 installed in openings 48 and 4| of plates 98 and 39. The rivet 52 includes a head 53 which is undercut at 54 and a shank '55. A cavity 58 is formed in the shank having an access opening thereto in the head 53 and closed at the shank end by a wall in the form of an inverted cone before expansion (see Figure'23). Near the end wall 51 the outer surface offthe shank 55 is provided with a groove 58 located in substantially the plane of therear face of wall 39.

When fluid pressure is introduced into this rivet 52 in the manner previously described, the pressure exerted against the end wall 51 causes it to flatten out into the shape shown in Figure 24. At the same time the shank of the rivet is expanded so that the shoulder formed by the groove 58 engages the rear face of plate 59 (due to the axial shortening of the rivet and rotation of n the end wall), and the remainder of the shank completely fills the openings 48 and 4|. One of the principal advantages of this form of rivet resides in the fact that the rivet need not be as long as those previously described. If desired, the groove 58 may be dispensed with, in which event it will be necessary to make the rivet slightly longer than that shown in Figure 23. If the groove is dispensed with the rivet will be expanded and embrace plates 38 and 39 in the same manner as has been described in connection with the other rivets heretofore mentioned. Except for from the form of end wall 51 and the groove 58, rivet 52 is like rivet la. As will be apparent, this form of rivet will exert a great radial pressure at the closed end, due to the rotation of end wall 51.

Figures 25 and 26 disclose a rivet 8|! substantially like the rivet 12 except for the fact fiat head 6|. This rivet has a shank 62 and is provided with a cavity 83 to which access is had through a small opening defined by the flange 54 formed by upsetting the head 6|. The head is undercut at 65 at the with the shank 52. This rivet is shown as used with a wall structure consisting -of a pair of plates 66 and 61 having openings 68 and 89 respectively. The plates are deformed as clearly shown adjacent the openings 68 and 69 to provide a recess on the front face of plate 68 to receive the head 8| of rivet 68. When the rivet 68 is expanded by the application of fluid pressure thereto in the manner previously described, the metal of the wall of the shank flows into the V-shaped groove formed between the two plates and against the edge of plate 61, as indicated at ll, 50 as to firmly secure the rivet to the plates and the plates together.

While only a typical form of flush head rivet is here shown, it will be understood that other forms may also be employed, and that the holes 68 and 69 may be drilled or reamed after the countersink has been formed in plates 66 and "la shown in Figures 11 and that it is provided with a junction of the head 81. In the latter case, groove III will be eliminated.

As will be readily apparent to those skilled in the art, the present invention is not limited to riveting two plates together, but may be used for other purposes. One such other application of the present invention is illustrated in Figure 27. As there shown, a rivet 88 is employed as a blind nut being secured to a wall 8|. The rivet 89 is generally similar to the rivet l0 previously described, and is secured to the wall 8| by the application of pressure to the interior thereof in the manner already described. In this instance.

the rivet is provided with a flat head 82 which is threaded interiorly thereof. to receive a fluid pressure applying nozzle such as the nozzle l5 shown in Figure 1. After the rivet has been expanded to the configuration shown in Figure 2'7, and the nozzle withdrawn, the threads contained in the head 82 may be employed to receive a screw threaded fastening device 83 which may be employed to detachably connect a part, such as the plate 84, to the plate 8|. In order to prevent the rivet 88 from rotating during the application thereto of the screw threaded device 83 the exterior surface of the rivet shank may be provided with longitudinal serrations 85 which form a biting engagement with the plate 8| when the rivet is expanded to lock the same thereto.

From the foregoing it will be seen that this invention provides a marked advance in the art of riveting. The rivets can be applied and will effectively hold the riveted parts together. The rivets can be fashioned economically. The riveting apparatus is compact and convenient and requires little skill for its operation.

The scope of the invention is indicated in the appended claims.

1. A rivet comprising a head and a shank having a cavity formed therein provided with a single access opening in the head, the head having an undersurface of relatively great area lying substantially in a plane at right angles to the axis of said shank but having an undercut covering a relatively small area in said plane adjacent the junction of the head with the shank to permit expansion of the shank adjacent said plane without necessitating expansion of the entire head.

2. A rivet comprising a head and a shank having a cavity formed therein provided with a single access opening in the head, the head having an undersurface of relatively great area lying substantially in a plane at right angles to the axis of said shank but having an undercut covering a relatively small area in said plane adjacent the junction of the head with the shank to permit expansion of the shank adjacent said plane without necessitating expansion of the entire head, and the shank being serrated along at least a portion of its length to bite into a wall structure or the like when the shank is inserted in a hole of proper size in such structure and is therafter expanded.

3. A rivet comprising a head and a shank having a cavity formed therein provided with a single access opening in the head, the head having an undersurface of relatively great area lying substantially in a plane at right angles to the axis of said shank but having an undercut covering a relatively small area in said plane adjacent the junction of the head with the shank to permit expansion of the shank adjacent said plane without necessitating expansion of the entirehead, and the shank being serrated along at least a guano REFERENCES CITED The following references are 01' record in the tile of this patent:

UNITED STATES PATENTS Number Name Date 221,447 Cornell Nov. 11, 1879 357,118 Dion Feb. 1, 1887 887,175 Abbott May 12, 1908 1,400,401 Allan Dec. 13, 1921 1,763,521 Holmes June 10, 1930 1,809,154 Beckner June 9, 1931 Number Number Name Date Lee May 24, 1932 Dreyer Sept. 27, 1932 Andeen July 10, 1934 Deems June 23, 1936 Giacchino Feb. 16, 1937 Febrey June 13, 1939 Hathom July 8, 1941 Moss July 13, 1943 FOREIGN PATENTS Country Date Norway July 21, 1930 France Mar. 28, 1923 Germany -2. Mar. 28, 1940 OTHER REFERENCES Engineering Record, vol. 63, Feb. 4, 1911, advertisement of MacArthur Concrete Pile and 20 Foundation Co. 

